Learning Objective:
By the end of this article, learners will be able to describe the anatomy, movements, neurovascular supply, and common clinical conditions associated with the proximal interphalangeal joint (PIPJ) of the hand.
Proximal Interphalangeal Joint (PIPJ) of the Hand
The proximal interphalangeal joint (PIPJ) is the articulation between the proximal and middle phalanges of the fingers. It is present in all digits except the thumb and functions as a synovial hinge joint, permitting flexion and extension that contribute to fine motor control and precision grip.
In this article, we explore the anatomy, neurovascular supply, movements, and clinical relevance of the PIPJ.
Anatomical Structure
Articulating Surfaces:
- Head of the proximal phalanx: Two curved condylar processes form a shallow groove.
- Base of the middle phalanx: Two concave sections form a raised ridge that fits into the proximal groove, providing intra-articular stability.
Joint Capsule:
- Each PIPJ is enclosed by a fibrous capsule, lined by a synovial membrane, and filled with synovial fluid.
Ligaments:
- Collateral ligaments (proper and accessory): Located on the radial and ulnar sides, they prevent excessive side-to-side movement.
- Arise from the head of the proximal phalanx and attach volarly to the middle phalanx.
- Each is accompanied by an accessory ligament attaching to the volar plate.
- Volar plate: A thick fibrocartilaginous structure in a U-shape across the base of the PIPJ, preventing hyperextension.
- Proximally attached via checkrein ligaments to the head of the proximal phalanx.
- Distally inserts onto the volar base of the middle phalanx.
Movements
The PIPJ, as a hinge joint, moves in one plane: flexion and extension.
Flexion:
- Normal range: 100–110°
- Primary muscle: flexor digitorum superficialis
- Secondary: flexor digitorum profundus (mainly flexes the DIPJ)
Extension:
- Normal: back to 0°
- Muscles involved: extensor digitorum, lumbricals, interossei, with the index finger assisted by extensor indicis
Neurovascular Supply
- Arterial supply: Palmar digital arteries
- Sensory innervation: Palmar digital nerves (branches of median and ulnar nerves)
Clinical Relevance
1. Central Slip Injury & Boutonnière Deformity
- The central slip tendon extends the PIPJ dorsally.
- Trauma (e.g., laceration, dorsal blow) or inflammation (e.g., arthritis) can damage it.
- Untreated injury → Boutonnière deformity: PIPJ flexed, DIPJ hyperextended.
2. PIPJ Dislocation
- Often occurs dorsally after hyperextension trauma.
- Commonly associated with volar plate injury.
- Management: Reduction and splinting; surgical repair if instability persists.
